Abstract
An intricate examination employing restriction fragment length polymorphism and virulence analyses has shed light on the population structure of Xanthomonas oryzae pv. oryzae, the notorious bacterial blight pathogen affecting rice crops across multiple Asian countries. In this comprehensive study, researchers utilized two pivotal DNA sequences from X. oryzae pv. oryzae, namely IS1112, which is an insertion sequence, and avrXa10, part of a critical family of avirulence genes, to probe the genomic characteristics of a substantial collection of 308 pathogen strains gathered from rice agriculture-rich countries such as China, India, Indonesia, Korea, Malaysia, Nepal, and the Philippines. The analysis revealed a consensus among three distinct clustering statistics, leading to the formation of five genetically diverse clusters. Genetic distances observed within these five clusters ranged from 0.16 to 0.51, indicating the degree of variation, while distances between clusters were markedly greater, spanning from 0.48 to 0.64. Interestingly, three of the five clusters comprised strains exclusively from a single nation, suggesting localized virulence characteristics, while the remaining two clusters exhibited strains from multiple countries, hinting at potential pathogen migration patterns. To accurately assess the pathogenicity, the pathotype of X. oryzae pv. oryzae was determined for 226 strains through inoculation tests on five rice differential cultivars. Notably, this evaluation revealed multiple pathotypes linked to each cluster, although certain pathotypes were exclusively associated with individual clusters. A significant observation emerged wherein strains isolated from South Asia, specifically Nepal and India, displayed virulence towards rice cultivars endowed with the bacterial blight resistance gene xa-5. In stark contrast, most strains collected from other regions remained avirulent to xa-5, highlighting a crucial aspect of regional resistance. The distinct regional differentiation of X. oryzae pv. oryzae clusters in Asia, coupled with the association of specific pathotypes with isolated clusters, strongly suggests the viability of tailored strategies focusing on regional resistance breeding and strategic gene deployment to combat this destructive rice pathogen.
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Selected References
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